RF inductance selection techniques
2016-12-06 16:36:19 Source:Shenzhen YLZ technology co., LTD Author:Admin Visit:302
Inductors, one of the most important components, are used in high-frequency analog circuits and signal processing for applications such as mobile phones, RFID, test equipment, GPS, radar, Wi-Fi and satellite radio. Typically, it can assume a number of major functions include circuit tuning, impedance matching, high-pass and low-pass filter, can also be used as RF chokes.
Electrons who choose to use RF inductors in their designs have a variety of options. To simplify this choice, we will discuss various types of inductance components and their common usage.
The use of RF inductors
Most electronic devices contain RF inductors. "In order to track animals, glass implants in the skin of our domestic animals contain an inductor," said Maria del Mar Villarrubia, a research and development engineer at Pramer. "Every time you start a car, two inductors Wireless communication takes place, one inside the car and the other inside the key.
However, as the omnipresence of such components, RF inductors have a very specific purpose. In a resonant circuit, these elements are typically used in conjunction with a capacitor to select a particular frequency (e.g., an oscillator circuit, a voltage controlled oscillator, etc.).
RF inductors can also be used for impedance matching applications, in order to achieve the impedance of the data transmission line balance. This is necessary to ensure efficient data transfer between the ICs.
When used as an RF choke, the inductor is connected in series in the circuit and acts as an RF filter. In simple terms, the RF choke is a low-pass filter that attenuates higher frequencies while the lower frequencies are unimpeded.
Q value is what
In discussing the inductor performance, Q value is the most important measure. The Q value is a measure of inductor performance and is a dimensionless parameter that compares the oscillation frequency to the energy loss rate.
"The higher the Q value, the closer the inductor performance is to the ideal lossless inductor," said Deryl J. Kimbro, senior product manager at Murata, Inc. "That is, it has better selectivity in resonant circuits."
Another benefit of high Q is low dissipation, which means that the inductor consumes less energy. A low Q value will result in a wider bandwidth and a lower resonant amplitude at and near the oscillation frequency.
Inductor value
In addition to the Q factor, the true measure of the inductance is, of course, its inductance. For audio and power applications, the inductance value is usually a few Henry, and high-frequency applications usually require a much smaller inductance, usually in the range of cents or micro-Hang.
The inductance value depends on several factors, including structure, core size, core material, and actual coil turns. The inductor has a fixed inductance value and an inductance value.
Other specifications
The inductance value is not the only important value. DC resistance, current, and self-resonant frequency (SRF) are some of the more useful specifications available in RF inductor data sheets.
According to del Mar Villarrubia, "Each feature can be a key consideration and determines other characteristics depending on the application, for example if the component is to be used in a tire pressure monitoring system, the inductance will be in a wide temperature range Of the stability is very important, and this requirement will determine the choice of core.
Rated current
In the choice of inductance, the operating current should be lower than the specification of the rated current. If the operating current exceeds the rated current, the product may be damaged.
DC Resistance (DCR)
Kimbro said DC resistance (DCR) and the rated current has a great relevance. Coil resistance as a benchmark, DC resistance is equivalent to the loss of the inductor. If the diameter of the winding increases, the DC resistance will decrease and the rated current will increase. The larger wire diameter reduces losses and improves current handling capability.
"DC resistance limits the amount of DC current that a device can transmit without overheating or without saturation," said Doug Lillie, product marketing manager for the Inductor Division at Vishay.
Self-Resonant Frequency (SRF)
Each winding in the inductor can be viewed as a capacitor plate. The overall effect of the capacitance between the turns and the coil and the core can be represented by a single capacitor in parallel with the inductor, called the distributed capacitance (Cd ). The resonant frequency of this parallel structure is called the self-resonant frequency (SRF).
"At this frequency, the inductor looks like a pure resistance with impedance, and if the frequency exceeds the self - resonant frequency, the capacitive reactance of this parallel structure becomes a major factor," Lillie said.
Laminated chip inductors
Multilayer chip inductors are fabricated using an integrated ceramic material. The ceramic material structure provides good performance at high frequencies, while the laminated chip process provides a wide range of inductance values.
The inductor value range of the laminar device is wider than that of the thin-film or air-core coil, but it is smaller than the inductance value range or the rated current of the wound-around element. Laminated chip technology is becoming increasingly popular due to its excellent electrical characteristics, especially its low cost.
Film inductors
Thin-film inductors are produced using photolithography processes that produce very accurate coil patterns on ceramic substrates to meet harsh inductor tolerances. Ceramic substrates make these inductors ideal for RF applications. However, the thin film inductor can transfer the current is small, and a limited range of values of inductance.
Wirewound inductors
Wirewound inductors are typically used in low frequency applications. Wirewound inductors are made of copper wire wound on a ceramic (alumina) core.
Wirewound inductors can provide good electrical characteristics due to their structure and material. The horizontal winding configuration allows for very small tolerances and small stray capacitance, while the copper wire makes the DC resistance very small, which increases the quality factor performance and the rated current.
Tapered inductance
Tapered inductors are for broadband and high-frequency applications, and its structure can broaden the bandwidth of the coil. The actual size of the tapered inductor is small, usually with a thin wire wound into, so stray capacitance smaller.
In ultra-wideband Bias-T devices, the tapered inductor also provides a DC bias extraction or injection path that isolates the power supply from the active device.
The choice of core
High frequency devices typically use a hollow or inert (i.e., ceramic) core. They provide better thermal performance than magnetic cores, but their inductance values are limited.
Medium frequency devices usually use iron core. The core does not saturate, but it does not provide a large inductance like a ferrite core. Low-frequency devices usually use ferrite cores. Ferrite cores should be avoided as much as possible because they will saturate at a small value of Idc and will be affected by temperature (ΔL / ΔT).
Manufacturers are also developing and using newer ferrite materials, such as amorphous and nanocrystalline materials.
Electrons who choose to use RF inductors in their designs have a variety of options. To simplify this choice, we will discuss various types of inductance components and their common usage.
The use of RF inductors
Most electronic devices contain RF inductors. "In order to track animals, glass implants in the skin of our domestic animals contain an inductor," said Maria del Mar Villarrubia, a research and development engineer at Pramer. "Every time you start a car, two inductors Wireless communication takes place, one inside the car and the other inside the key.
However, as the omnipresence of such components, RF inductors have a very specific purpose. In a resonant circuit, these elements are typically used in conjunction with a capacitor to select a particular frequency (e.g., an oscillator circuit, a voltage controlled oscillator, etc.).
RF inductors can also be used for impedance matching applications, in order to achieve the impedance of the data transmission line balance. This is necessary to ensure efficient data transfer between the ICs.
When used as an RF choke, the inductor is connected in series in the circuit and acts as an RF filter. In simple terms, the RF choke is a low-pass filter that attenuates higher frequencies while the lower frequencies are unimpeded.
Q value is what
In discussing the inductor performance, Q value is the most important measure. The Q value is a measure of inductor performance and is a dimensionless parameter that compares the oscillation frequency to the energy loss rate.
"The higher the Q value, the closer the inductor performance is to the ideal lossless inductor," said Deryl J. Kimbro, senior product manager at Murata, Inc. "That is, it has better selectivity in resonant circuits."
Another benefit of high Q is low dissipation, which means that the inductor consumes less energy. A low Q value will result in a wider bandwidth and a lower resonant amplitude at and near the oscillation frequency.
Inductor value
In addition to the Q factor, the true measure of the inductance is, of course, its inductance. For audio and power applications, the inductance value is usually a few Henry, and high-frequency applications usually require a much smaller inductance, usually in the range of cents or micro-Hang.
The inductance value depends on several factors, including structure, core size, core material, and actual coil turns. The inductor has a fixed inductance value and an inductance value.
Other specifications
The inductance value is not the only important value. DC resistance, current, and self-resonant frequency (SRF) are some of the more useful specifications available in RF inductor data sheets.
According to del Mar Villarrubia, "Each feature can be a key consideration and determines other characteristics depending on the application, for example if the component is to be used in a tire pressure monitoring system, the inductance will be in a wide temperature range Of the stability is very important, and this requirement will determine the choice of core.
Rated current
In the choice of inductance, the operating current should be lower than the specification of the rated current. If the operating current exceeds the rated current, the product may be damaged.
DC Resistance (DCR)
Kimbro said DC resistance (DCR) and the rated current has a great relevance. Coil resistance as a benchmark, DC resistance is equivalent to the loss of the inductor. If the diameter of the winding increases, the DC resistance will decrease and the rated current will increase. The larger wire diameter reduces losses and improves current handling capability.
"DC resistance limits the amount of DC current that a device can transmit without overheating or without saturation," said Doug Lillie, product marketing manager for the Inductor Division at Vishay.
Self-Resonant Frequency (SRF)
Each winding in the inductor can be viewed as a capacitor plate. The overall effect of the capacitance between the turns and the coil and the core can be represented by a single capacitor in parallel with the inductor, called the distributed capacitance (Cd ). The resonant frequency of this parallel structure is called the self-resonant frequency (SRF).
"At this frequency, the inductor looks like a pure resistance with impedance, and if the frequency exceeds the self - resonant frequency, the capacitive reactance of this parallel structure becomes a major factor," Lillie said.
Laminated chip inductors
Multilayer chip inductors are fabricated using an integrated ceramic material. The ceramic material structure provides good performance at high frequencies, while the laminated chip process provides a wide range of inductance values.
The inductor value range of the laminar device is wider than that of the thin-film or air-core coil, but it is smaller than the inductance value range or the rated current of the wound-around element. Laminated chip technology is becoming increasingly popular due to its excellent electrical characteristics, especially its low cost.
Film inductors
Thin-film inductors are produced using photolithography processes that produce very accurate coil patterns on ceramic substrates to meet harsh inductor tolerances. Ceramic substrates make these inductors ideal for RF applications. However, the thin film inductor can transfer the current is small, and a limited range of values of inductance.
Wirewound inductors
Wirewound inductors are typically used in low frequency applications. Wirewound inductors are made of copper wire wound on a ceramic (alumina) core.
Wirewound inductors can provide good electrical characteristics due to their structure and material. The horizontal winding configuration allows for very small tolerances and small stray capacitance, while the copper wire makes the DC resistance very small, which increases the quality factor performance and the rated current.
Tapered inductance
Tapered inductors are for broadband and high-frequency applications, and its structure can broaden the bandwidth of the coil. The actual size of the tapered inductor is small, usually with a thin wire wound into, so stray capacitance smaller.
In ultra-wideband Bias-T devices, the tapered inductor also provides a DC bias extraction or injection path that isolates the power supply from the active device.
The choice of core
High frequency devices typically use a hollow or inert (i.e., ceramic) core. They provide better thermal performance than magnetic cores, but their inductance values are limited.
Medium frequency devices usually use iron core. The core does not saturate, but it does not provide a large inductance like a ferrite core. Low-frequency devices usually use ferrite cores. Ferrite cores should be avoided as much as possible because they will saturate at a small value of Idc and will be affected by temperature (ΔL / ΔT).
Manufacturers are also developing and using newer ferrite materials, such as amorphous and nanocrystalline materials.
